Analysis of plasmid associated cell material provides a powerful method for discovering and analyzing critically low amounts of cell materials involved in plasmid replication and segregation. Likewise, plasmid and host mutants defective in plasmid associated materials provide another very useful variation of the above approach. Genetic techniques are used to obtain mutants defective in plasmid maintenance or mutants overactive in plasmid replication. The first class of mutants is obtained by selection for loss of plasmid transmission at restrictive growth conditions and the second class is obtained by selecting for colonies with increased dosages of plasmid genes. The first class of mutants should represent both replication and segregation defective mutants. Recently, we have combined standard physiochemical assays for folded chromosome and F sex factor physical structures in a way that demonstrates a physical connection between these two replicons. We have probably isolated the unit of segregation. Physicochemical, enzymic, and physiological studies are proposed which will shed insight on the biochemical nature of this physical connection. Bacteria of the above mutant classes will be examined for normal parameters defined for unit of segregation. Additionally, other plasmid systems with properties closely related to F (e.g. R factors) or distantly related to F (e.g. lambda dv, col E1) will be examined for their presence in the unit of segregation to seek understanding of their manner of distribution at cell division. Appropriate biochemical analysis will be performed if these associations are found. Plasmid and chromosome DNA-membrane complexes will be purified after separation from the bulk of non-complexed DNA by digestion with restriction endonuclease. The complexed DNA's will be tested for unique sequences by DNA: DNA hybridization. Likewise, DNA- membrane complexes from different DNA systems will be tested for differences in protein composition by SDS-acrylamide electrophoresis. Protein profiles from both mutant and normal systems will be examined.